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The paper deals with the origin, evolution and taxonomic position of peculiar parasitic platyhelminths of the group Aspidogastrea. A great attention is given to the character of affinities between aspidogastrids and trematodes. A definite morphological similarity between the both groups is due, according to the author, to the origin from common ancestors. However, their further evolution proceeded in different ways.

In this paper experimental frequency distributions of the hosts according to the number of helminths are compared to the theoretical negative binomial distribution. Good fitting is in the case of mice invasion with the cestode Hymenolepis fraterna and that of moles with the nematode Heligmosomum costellatum. A theoretical substantiation of the correctness of conditions of the pattern within certain ranges of the invasion intensity is given.

Dragonflies of the family Aeschnidae (Aeschna grandis, A. cyanea, A. juncea, Anax imperator) were found to be infected (invasion extensity 63.5%) with progenetic metacercariae of Prosotocus confusus. Observations were carried out in the lake Karagaily (Bashkiria, South Ural, USSR) where the definitive hosts of this trematode, members of the Anura order, are absent. Under experimental conditions metacercariae remain in the intestine of Rana terrestris not more than 24 hours. When placed in water they excrete eggs containing miracidiums. The intermediate host is the mollusk Bithynia tentaculata. Eggs of the parasite are spread over the water body mainly by birds eating up the infected dragonflies.

A new species of nematodes, Heterotylenchus simplex sp. n., was found in zoophilous flies of Morellia simplex caught from cows in the Bakhchisaray region of the Crimea. The above species differs from all known ones of the genus Heterotylenchus in the presence of the quadricolumella in parthenogenetic females and rudiment of the posterior uterine branch in gamogenetic females. H. simplex is close in its biology and ecology to H. autumnalis and in its morphology — to H. aberrans.

The paper describes neurosecretion in six species of parasitic nematodes with different ecological peculiarities. The data are given on the morphology and topography of neurosecretory cells.

A parallel study of 25 strains of Flagellata isolated from 6 species of sand flies was carried out by means of biotest, Adler's serological method modified by Safjanova and "temperature" method. It was established that the use of several methods for the identification of Leishmania allows more reliable results to be obtained. The differentiation of strains with the "temperature" method can be done over a relatively shorter period of time.

In 14 days after the intraperitoneal infection of mice with 30% brain emulsion of white mice or of newly-born rats in the peritoneal liquid there were found spores of Nosema sp. 5.37±0.08X3.04±0.07 in size. The subsequent attempts to passage this organism on the mice by adminestering into them the suspension from the brain and internal organs of infected animals yielded ho results. The material for diagnosing on microsporidians of mammals is being discussed.

On the basis of observations undertaken in Azerbaijan and available literary data the author considers the hypotheses concerning the reasons causing the delay of the Ist instar larvae development and determining the age structure changes in populations of Oestrus ovis L. within a year. The main reasons are as follows: factors depending on the population density at the larval phase, the light day duration within the life cycle of the botfly females.

Eusimulium schogakii Rubz. was recorded from the USSR for the first time. The description of its larvae and some additional data on the taxonomy of males, females and pupae are given. The hatching sites, distribution areas and the pupation periods are indicated.

Histological studies of Ceratophyllus consimilis infected with Salmonella typhimurium have shown that the microbes are preserves along the whole extent of the alimentary canal, especially in the midgut and pyloric portion. Bacteria are concentrated in the gastral cavity; in addition, they were found to penetrate the alimentary epithelium cells and pyloric valve tissue. The number of microbes and their distribution in the intestine undergo great variations that depends largely on the insects feeding rhythm. During bloodsucking a "lavement" of the alimantary canal takes place; as a result, numerous microbes accumulated here are periodically excreted outside. The infection with Salmonella typhimurium is often accompanied by pathological changes in fleas that is expressed in the destruction of the midgut epithelium and pyloric valve tissue.

The paper presents data on the specific composition of arthropods, nidicols of burrows, from the colonies of the great gerbil in the Caspian part of the Ural-Embinsk inter-river area. The quantitative ratio between different ecological groups of arthropods is given. The structure of microbiocoenosis is analysed.

A study was carried out of the variability of mites collected from 6 species of birds as follows: Larus argentatus Pontopp., L. minutus Pall., Gelochelidon nilotica Gm., Clnlidonias leucoptera (Temm.), Ch. nigra (L.) and Sterna hirundo L. Structural peculiarities characteristic of the parasites of the above species have been revealed. The mites from St. hirundo were isolated into a distinct species, Larinyssus substerna sp. n., which is most close to L. sterna Fain, 1972. The new species differs from L. sterna in a smaller size of gnathosoma and chelicerae, lesser number of hypostomal setae and the presence of pigidial shields.

2213 lice of Neohaematopinus palaearctcus Ols. were collected from 152 of 865 examined specimens of Marmota caudata Geoffr. from different vertical zones of Tadjikistan. The long-tailed marmot is characterized by a moderate or poor infestation with lice. In the subalpine zone, where the number and density of these animals in rather high, the infestation rate is greater than that in the brushwood zone. In spring after hibernation the infestation of M. caudata is very low. Within the reporoduction period the infestation with lice increases, the latter begin to reproduce intensively. During the preparation for hibernation the infestation rate falls due to a less intensive reproduction of lice. There are no distinct differences in the infestation rate of long-tailed marmots belonging to different age groups since there are constant contacts between the individualstof the colony. Only reproducing females live together with brood by themselves, differ in moulting periods and in a greater intensity of invasion during reproduction.

This paper contains a description of the morphology of the larvae and pupae of Leptoconops mediterraneus Kieff. from Kazakhstan. Some observations on the biology of this species are given.

63 nests of 11 species of birds were examined in the mid-taiga forests of Prikamje from 1971 to 1973. 710 specimens of midges were caught within this period. 8 species of midges attacked birds. Of them the most abundant was Culicoides cubitalis Edw. (62.8%). Rather numerous were C. sajanicus Mirz. (14.9%) and C. reconditus C. et P.-C. (11.9%). The other species were few in number or rare. In closed nests C. reconditus C. et P.-C. (42.1%) prevailed. One fourth of caught females were with blood (26.9%). The highest per cent of engorged females was found in C. sajanicus Mirz. (58.3%).

The mosquitoes of Culex pipiens molestus first recorded from Leningrad as far as 30 years ago have been reported from the settlements of the Leningrad district since 1965. The most northern point of their occurrence is marked at 60°45' N and is removed from Leningrad for over 120 km. Such spread of mosquitoes to new settlements is associated with the development of multistory housing construction in the country and delivery of imagos from Leningrad to the settlements of the district by means of transport.

The paper reports on the first case of discovery of one Lichomolgidae member (Copepoda, Суclopiida) on the gills of Trachurus trachurus (Linne). The copepod Paramacrochiron sewelli Reddiah. 1968, known earlier as a commensal of Lychnorhiza malayensis Stiasny, turned out to be a parasite of this fish. A brief description of this crustacean is given.

Summary is absent.